How GPS And OnStar Work

March 31, 2003

GPS technology works by using radio signals from 24 satellites orbiting at an altitude of 10,900 nautical miles above the earth. Each satellite calculates how long it takes a radio signal from the satellite to reach a specific vehicle, then calculates the time to do so using the speed of light (186,000 miles/s). Both the satellite and the vehicle's GPS receiver generate the same pseudorandom coded signal.

OnStar calculates the time the signal travels by comparing how late the satellite's code is with respect to the receiver. That time difference is then multiplied by 186,000 miles/s, giving the vehicle's distance from one satellite. For the most accurate measurement of vehicle location, OnStar uses measurement from four of the 16 satellites.

When communicating with an OnStar Call Center, the vehicle-identification number (VIN) and the user's account number are transmitted, as are the vehicle's make, color, and model year (see the diagram).

About the Author

Roger Allan

Roger Allan is an electronics journalism veteran, and served as Electronic Design's Executive Editor for 15 of those years. He has covered just about every technology beat from semiconductors, components, packaging and power devices, to communications, test and measurement, automotive electronics, robotics, medical electronics, military electronics, robotics, and industrial electronics. His specialties include MEMS and nanoelectronics technologies. He is a contributor to the McGraw Hill Annual Encyclopedia of Science and Technology. He is also a Life Senior Member of the IEEE and holds a BSEE from New York University's School of Engineering and Science. Roger has worked for major electronics magazines besides Electronic Design, including the IEEE Spectrum, Electronics, EDN, Electronic Products, and the British New Scientist. He also has working experience in the electronics industry as a design engineer in filters, power supplies and control systems.

After his retirement from Electronic Design Magazine, He has been extensively contributing articles for Penton’s Electronic Design, Power Electronics Technology, Energy Efficiency and Technology (EE&T) and Microwaves RF Magazine, covering all of the aforementioned electronics segments as well as energy efficiency, harvesting and related technologies. He has also contributed articles to other electronics technology magazines worldwide.

He is a “jack of all trades and a master in leading-edge technologies” like MEMS, nanolectronics, autonomous vehicles, artificial intelligence, military electronics, biometrics, implantable medical devices, and energy harvesting and related technologies.